Mobile devices, such as but not limited to personal data appliances, cellular phones, radios, pagers, lap top computers, and the like are required to operate for relatively long periods before being recharged. These mobile devices usually include one or more processors as well as multiple memory modules and other peripheral devices.
Modern integrated circuits are manufactured by applying highly complex manufacturing process. These manufacturing processes are characterized by deviations in impurity concentration densities, oxide thickness, diffusion depths, difference in transistors dimensions and the like.
An integrated circuit includes a die. Multiple dies (also known as dices) are included in a single wafer. Wafers are usually manufactured in lots. Transistor parameters (such as delay and leakage current) can differ from one lot of wafers to another, from one wafer to another and even from one die to another.
An integrated circuit is regarded as operational if it was manufactured by a manufacturing process that is within a process window. The process window is delimited by a best case scenario and by a worst case scenario.
Differences in the delay of transistors that belong to the same integrated circuit can cause timing violations such as setup violations and hold violations.
These timing differences are more noticeable in high threshold voltage low leakage transistors that are usually used in mobile devices.
The delay difference between transistors that belong to the same integrated circuit increases as the supply voltage level (supplied to these transistors) decreases. The delay difference between different transistors of a certain integrated circuit is not known in advance and is also responsive to variables such as ambient temperature. In order to guarantee the proper functionality of the integrated circuit the supply level is not lowered (when the integrated circuit is active and not idle) below a supply voltage lower threshold.
This supply voltage lower threshold is defined in response to a possible existence of best case scenario transistors and worst case scenario transistors within the integrated circuit.
Each integrated circuit is manufactured by an instance of the manufacturing process. In most cases the transistors within the integrated circuit belong to a small subset out of all the possible transistors that can be manufactured within the relatively wide process window. Accordingly, the difference between the parameters of different transistors that belong to the same integrated circuit is smaller than the possible difference between the parameters of worst case scenario transistors and best case scenario transistors.
This supply voltage lower threshold causes a waste of power, as it is usually above the supply voltage level that can actually be supplied to the integrated circuit, without resulting in timing violations.
Silicone on Insulator (SOI) circuits are characterized by reduced transistors parameter variation but they have their own drawbacks. U.S. Pat. No. 6,624,663 of illustrates a prior art SOI circuit.
There is a need to estimate parameter variations of transistors that belong to an integrated circuit.